1. Field of the Invention
The present invention relates to a color ink sheet for thermal transfer to be used in color recording by thermal transfer, and more particularly, to color ink sheet for thermal transfer for a color printer comprising an electronic component such as a thermal head.
2. Description of the Prior Art
A thermal transfer recording method has been known as a method of color recording of color image information from a CRT output terminal of a television, video tape recorder, electronic camera, personal computer or the like through electric signals.
A color ink sheet for thermal transfer (hereinafter referred to as the "ink sheet") used in this recording method comprises solid ink layers of at least three colorants, i.e. yellow, magenta and cyan colorants, which can be thermally transferred, the solid ink layers being arranged face to face repeatedly on a base substance such as a paper or plastic sheet.
The inks are transferred onto a recording paper by fusing the same with the heat of a thermal head controlled by image signals or by sublimating or evaporating a subliming dye in the ink. The transfer is effected 1 to 3 times for each of the three colors of yellow, magenta and cyan colorants on same recording paper to record the color image.
The color reproducibility of the color image recorded on the recording paper as compared with the original image varies mainly depending on the colorant contained in the ink layer of the ink sheet. The colorants which are transferred by the fusion of the ink (hereinafter referred to as "fusion-type") include a dye and pigment which are used widely as ordinary colorants. The colorants which are transferred by the sublimation or evaporation of the dye in the ink (hereinafter referred to as "sublimation-type") include a disperse dye having a sublimation function of a sublimating dye such as basic dye.
However, sufficient care is not always taken of the hue or chroma after the transfer of the colorants on the recording paper. Thus, the color specification range or color expression range of the image transferred by means of the current link sheet is narrower and the color reproducibility is lower than those realized by the ordinary color printing, color photography or color CRT image.
Examples of colorants used after the transfer of the image onto the recording paper by means of the thermal transfer color ink sheet are given in a report of Inada, Wakatsuki and Takahashi entitled "Color hard copy of optical photography system" in the proceeding of The First Non-Impact Printing Technique Symposium (promoted by the Society of Electrophotography of Japan on July 24, 1984) and also in Japanese Patent Laid-Open Publication Nos. 220788/1983, 93390/1984 and 93391/1984.
However, the above prior documents contain no disclosure with respect to a spectral reflectance aspect. Furthermore, a color ink sheet shown in the above prior documents has a narrow color specification range and a low color reproducibility as a whole.